First magmatism in the New England Orogen, Australia: Forearc and arc-backarc components in the Bakers Creek Suite gabbros
Seann J. McKibbin1,2,a, Bill Landenberger1, and Mark C. Fanning21School of Environmental and Life Sciences, University of Newcastle, Uni versity Drive, Callaghan, 2308, Australia 2Research School of Earth Sciences, Australian National University, Bldg. 61, Mills Road, Canberra, 0200, Australia anow at: Analytical, Environmental and Geo-Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, Bru ssels 1050, Belgium
Received: 20 Aug 2016 – Accepted for review: 31 Aug 2016 – Discussion started: 31 Aug 2016
Abstract. The New England Orogen, Eastern Australia, was established as an outboard extension of the Lachlan Orogen through the migration of magmatism into the forearc basin and accretionary prism. Widespread S-type granitic rocks of the Hillgrove and Bundarra Supersuites represent the first pulse of magmatism, followed by I- and A-types typical of circum-Pacific extensional accretionary orogens. Associated with the former are a number of small tholeiite-gabbroic to intermediate bodies of the Bakers Creek Suite, which are a heat source for production of granitic magmas and potential tectonic markers indicating why magmatism moved into the forearc and accretionary complexes, rather than rifting the old Lachlan Orogen arc. The Bakers Creek suite gabbros capture an early (~ 305 Ma) forearc basalt-like component with low Th/Nb and with high Y/Zr and Ba/La, recording melting in the mantle wedge with little involvement of a slab flux and indicating forearc rifting. Subsequently, arc-backarc like gabbroic magmas (305–304 Ma) were emplaced followed by diverse magmatism of mixed compositions leading up to the main S-type granitic intrusion (~ 290 Ma). This trend in magmatic evolution implicates forearc and other mantle wedge melts in the heating and melting of fertile accretion complex sediments and relatively long (~ 10 Myr) timescales for such melting.
McKibbin, S. J., Landenberger, B., and Fanning, M. C.: First magmatism in the New England Orogen, Australia: Forearc and arc-backarc components in the Bakers Creek Suite gabbros, Solid Earth Discuss., doi:10.5194/se-2016-123, in review, 2016.